1. Field of the Invention
The present invention relates to an automatic metal solution dilutor, and more particularly, it relates to an automatic metal solution dilutor automatically diluting a concentrated metal solution from the order of percentage to the order of ppm in high accuracy.
2. Description of the Background Art
According to a general dilution method, an object metal pulverulent body or a concentrated metal solution of the order of percentage is manually metered, mixed with a diluent liquid to be diluted to a required concentration and a required quantity, and fed to a feeder.
However, this method employs an around-the-clock system and dilution errors result from manual dilution by a plurality of operators. The metal pulverulent body or the metal solution is not fed with in-line concentration control, and hence concentration fluctuation caused by manual dilution errors or unexpected inclusion of water resulting from an equipment failure or breakdown leads to sudden concentration abnormality such that the diluted solution cannot be stably fed to the feeder by 100%.
In concentration measurement, a high-quality analyzer such as an atomic absorption spectrophotometer or an ICP analyzer is employed for analyzing the metal concentration of the order of ppm (parts per million: 10−6). Such a high-quality analyzer must be set in a humidity-controlled control room or the like under an excellent environmental condition in consideration of assurance of analytical accuracy or management of the analyzer, and a measured solution must be diluted to the order of ppb (parts per billion: 10−9).
A method of concentration measurement employing neutralization titration is also carried out. However, this method requires a large-scale apparatus and a long time for concentration measurement. When a liquid dilution tank of at least several 10 liters is provided, therefore, this method can be employed with no problem. However, it is difficult to apply this method to a dilutor non-periodically feeding a diluted solution having a required concentration and a required quantity.
The following techniques disclosed in Japanese Patent Laying-Open Nos. 6-307994 (1994) and 7-167756 (1995) have been confirmed as conventional dilutors:
Japanese Patent Laying-Open No. 6-307994 discloses a dilutor diluting a fed stock solution mixed with a diluent liquid in a vessel and feeding the diluted solution to a remote measuring device with compressed gas.
The technique disclosed in this gazette relates to a liquid dilutor applied for diluting a liquid having a high metal ion concentration readily depositing crystals. According to this technique, the diluent liquid and a concentrated liquid are metered, thereafter fed, stirred/diluted in a tank and fed to a feeder with compressed air after completion of the dilution.
Japanese Patent Laying-Open No. 7-167756 discloses a method of inputting absorbance of a stock solution and a diluent liquid with a densitometer measuring absorbance or the like, operating a dilution magnification for the liquid to be diluted with the diluent liquid and diluting the liquid without requiring strict measurement of the volume or the weight.
The technique disclosed in this gazette relates to an automatic liquid dilutor applied to water treatment chemicals for a power plant or the like. This technique employs a method of calculating a dilution ratio from a result of measurement with the densitometer performing calculation with reference to absorbance.
According to the dilutor disclosed in Japanese Patent Laying-Open No. 6-307994, however, it is difficult to accurately meter a required liquid volume due to a metering method of introducing and charging the stock solution and the diluent liquid in a meter of a constant volume and thereafter feeding the same to a dilution tank.
Further, this method depends on only metering without executing concentration control, disadvantageously leading to inferior reliability of the prepared diluted solution.
The apparatus disclosed in Japanese Patent Laying-Open No. 7-167756 dilutes ammonia to the order of ppb, and hence it is disadvantageously necessary to add a 1% ethanol solution serving as an index substance.
In this analyzer executing weighing only through a valve switching time, weighing is so dispersed that stable dilution cannot be performed.